This morning Box announced that it will integrate its cloud storage solution into Microsoft’s popular Office 365 productivity suite. The company also indicated that its ‘Business’ SKU will no longer have a file storage cap, joining its ‘Enterprise’ SKU in having unlimited storage attached to each user’s account.

The storage play is simple: As the amount of space given to free users of cloud storage expands, the quantity provided to paying customers has risen to infinity. Dropbox‘s Business plan offers, for example, “as much as needed,” according to its page. Previously, Box’s ‘Business’ SKU had a one terabyte limit.

Speaking of Office 365, Box has a neat jig in mind: Supporting it. Why would Box decide to integrate with Office 365, and thus put some of its enterprise heft behind Microsoft’s cloud productivity play that is widely associated with OneDrive, a Box competitor? The reason is fun, actually.

Let’s start slowly and build: Box has quite a lot of enterprise mind-share, which it likes to convert to market-share by employing a large salesforce (Reference: see its most recent cost breakdown). Microsoft’s Office 365 product has done, to quote Box CEO Aaron Levie from a short call yesterday, “incredibly well.” And, as we have argued time and again, file storage services without editing tools — and the other way around —are moot. Thus, if you are Box, and you don’t have a spare billion to sink into writing your own productivity suite, and your largest customers are already Office — if not yet Office 365 — facing, what do you do? Integrate with Office 365.

Box’s integration into Office 365 is what you would expect, with its file system finding a place inside Microsoft’s software, so that users of Box’s two most costly SKUs — sorry, free and ‘Pro’ users — can access and edit files that they have either stored in Box already, or create new files that they can then place into Box. Box will also integrate into Outlook, and, eventually, into Office Online.

It’s a neat sidestep. Why build when you can integrate? And, given that Microsoft has open APIs that allow for this sort of thing, Box can pretty easily shimmy into the mix and, presto, the service now undergirds the leading cloud productivity product.

Microsoft, despite preferring that business customers use its full stack, will likely see more buy-in of its premier subscription service, so it can’t cry too heavily into its hands that OneDrive might lose market share among enterprise customers.

Box’s Office 365 integration will be released into beta “this Fall.” Expect Box competitors to follow in its footsteps.

On a tangent, Levie has written for TechCrunch in the past, a passage of which caught my eye:

Questions abound. Are there files in the future or not? Do we use Microsoft Office anymore? Are we just in a multi-year transition period before we’re completely cloud? If I store a document in Google, how do I get to it from my Mac? If I store a photo in my iCloud, how do share it with someone on a Windows phone?

However, with the rise of tablets, office workers have suddenly noticed that they don’t need Office anymore. All they need is an email app, a notepad, and something like Dropbox. You can open Office docs on any device, you can edit text on nearly any tablet, and $9.99 gets you a capable word processor on the iPad. In short, Office is becoming irrelevant.